Dissertation (MMED General Surgery)Secondary Peritonitis is a familiar condition surgeonfaces in daily clinical practice with high morbidity, mortality, and poor prognosis. Its outcome depends on the interface of many factors, including patient, surgeons and institutional factors, etc.Early initiation of specific therapeutic procedures predicts a good outcome. There is no locally acceptable surgical outcome predictor to minimize morbidity and mortality and improve resuscitation outcome for high-risk patients. therefore, early assessment by scoring systems will influence management and prognosis. This is a prospective cross-sectional hospital-based study conducted in UDOM affiliated teaching hospitals using 73 consecutive patients (51 males, 22 female) having secondary Peritonitis from May 2019 to April 2020. We applied both scoring systems (APACHE II and MPI) to patients before Laparotomy. We organized Patients into three groups according to their scores. We recorded the outcomeand evaluated the accuracy of the two systems. In the APACHE II system, we recorded no mortality among patients with scores less than ten and a group with score 10 - 20. Mortality was 100% in patients with a score of more than 20. Similarly, there was no mortality in the group of patients with MPI score less than 15, while it was 10% and 90% in the patients with scores16 - 25 and more than 25, respectively. Both scoring systems were accurate in predicting mortality; however, the MPI score is simple to apply and use while APACHE II is more accurate and has better and is more useful.Further research in future studies can be done with larger samples, matched ages, and sex.